We investigate the temporal ownership boundary that exists in the sharing economy. We find that temporal factors play an important role in the decisions of collaborative contribution. A collaborative contributor need not only consider the engagement duration and the potential income, but also the holding/inventory/maintenance costs during its ownership. We define the temporal ownership boundary as the limit when the owner is indifferent of transferring the ownership from its current in-usage or sharing status. By this definition, we can decompose a merchandise as two substitute goods: the ownership good and the transferring good. The ownership good can be consumed or shared by the owner. The transferring good can either be given as a gift or be resold for an income. The temporal ownership boundary can be found by considering the owner's holding cost, various transaction costs, and the potential income from the sharing economy activities. We find that there exists various conditions when this boundary may lean towards sharing, gift giving or reselling.